Battery plates having rounded lower corners

ABSTRACT

A process for cutting a moving strip to form a series of plates, such as battery plates, includes the initial step of transporting the strip past a rotary divider including a cutter having radial blades configured to cut the strip into the plates. The cutter further has a set of blades for cutting individual pieces from the strip, which pieces are not part of the plates. As the cutter blades cut the strip to form the plates and pieces, a vacuum system applies suction to draw the pieces cut from the strip inwardly into the cutter through holes in the cutter, and then out of the cutter. The holes are each located adjacent each one of the corresponding blades and are shaped and positioned to permit the cut-away piece to pass through. In a preferred embodiment, the vacuum system includes a pair of vacuum manifolds that apply suction at opposite ends of the cylindrical cutter. An apparatus for carrying out the foregoing process accordingly includes a rotary divider as described above provided with a vacuum system. Battery plates made according to the foregoing process are improved in that the two lower corners have a rounded shape lacking a sharp edge which tends to tear an adjacent separator. Such a plate may be inserted bottom end first into a separator envelope to form a plate element for use in a lead-acid battery.

TECHNICAL FIELD

The present invention relates to the manufacture of plates from a movingstrip by cutting the strip, particularly to the manufacture of batteryplates for use in lead-acid batteries.

BACKGROUND OF THE INVENTION

A plate for a lead-acid battery is conventionally made by applying abattery paste to a conductive support such as a lead alloy grid. Thepaste is made from lead oxide, sulfuric acid and water. The lead oxidereacts with the sulfuric acid to form mono-, tri- or tetrabasic leadsulfate(s). Dry additives such as fiber and expander may be added. Themixture is then dried and water is re-added to form a paste of thedesired consistency. The paste is applied to the lead grid, and thepasted plates are then flash-dried and cured at an elevated temperatureand humidity to oxidize free lead and adjust the crystal structure ofthe plate. After curing, the plates are assembled into batteries andelectrochemically formed by passage of current to convert the leadsulfate or basic lead sulfate(s) to lead dioxide, thereby forming theactive lead material.

The lead alloy grid is made in a multistage process in which molten leadalloy is cast to form a strip. The strip is expanded to form meshelements for grids, and the paste is then applied. Liner papers areapplied to the surfaces of freshly pasted plates during the pastingoperation to facilitate handling and stacking. Individual plates areformed by passing the pasted strip through a rotary divider that cutsthe outlines of the individual plates on the moving strip. To ensureproper registration for cutting, the strip is formed during expansionwith a series of regularly spaced central recesses that are engaged bylugs of a drive roller associated with the divider. The cut plates arethen flattened, flash-dried, and stacked for later use in lead-acidbattery manufacture.

The battery grids each take the form of a generally rectangular framesupporting a mesh of grid elements onto which the paste is applied. Theframe has a pair of upper corners and a pair of lower corners, and anelectrically conductive tab extending from a location between the twoupper corners. In one common battery design, every other plate in thebattery stack is inserted into an envelope made of a separator materialsuch as submicro polyethylene. The sides of the envelope act asseparators between the plate in the envelope and the two adjoiningplates in the battery stack.

In assembling a battery of this kind, it is necessary to insert thebattery plate bottom-first into the open end of the envelope so that theconductive tab at the top of the plate extends out of the envelope.However, the bottom corners on the battery plates are sharp, and willsnag and tear the separator material between the positive and negativeplates, causing an electrical short within the battery and reducingbattery life. Bending or vibration of the plate disposed in the envelopeduring assembly or use can also cause tearing, and the problem is notconfined to envelope-style separators.

Use of battery plates with rounded bottom corners would eliminate thesnag and tearing of separators, but no practical process has beenproposed for producing rounded corners on such battery plates. Inparticular, any process wherein the rotary divider cuts off cornersresults in small pieces of trim (scrap) that are severed from the strip.These pieces, if left on the strip after cutting, can come loose andcause cutting die failure on the divider and can lead to battery failureif the pieces are carried over and inadvertently incorporated into thefinished battery. The present invention addresses these problems byproviding a system for cutting the rounded corners and then removing thepieces during continuous plate manufacture.

SUMMARY OF THE INVENTION

A process for cutting a moving strip to form a series of plates, such asbattery plates, initially involves transporting the strip past a dividerhaving a rotary cutter with a first set of blades extending radiallytherefrom configured to cut the strip into the plates, and a second setof radial blades for cutting individual pieces from the strip. As theblades cut the strip to form the plates and pieces, a vacuum systemapplies suction to draw the pieces cut from the strip inwardly into thecutter through holes in the cutter, and then out of the cutter. Theholes are each located adjacent one of the corresponding cutter bladesof the second set and are shaped and positioned to permit the cut-awaypiece to pass through. In a preferred embodiment, the vacuum systemincludes a pair of vacuum manifolds that apply suction at opposite endsof the cylindrical cutter.

An apparatus for carrying out the foregoing process accordingly includesa rotary divider having a cylindrical cutter configured to cut the stripinto the plates, including a second set of blades for cutting individualpieces from the strip as described above, and a vacuum system thatapplies suction to draw the pieces cut from the strip inwardly into thecutter through the holes in the cutter, and then out of the cutter.

According to a further aspect of the invention, a conventional batteryplate as described above is improved in that the two lower corners havea rounded shape lacking a sharp edge which would tend to tear anadjacent separator. Such a plate may be inserted bottom end first into aseparator envelope to form a plate element for use in a lead-acidbattery.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numerals denote like elements, and:

FIG. 1 is a schematic diagram of an overall process for making batteryplates in which the process of the invention is included, with the shapeof the strip at each stage shown below;

FIG. 2 is a schematic diagram of a vacuum system used with a divideraccording to the invention;

FIG. 3 is a schematic side view of the divider and flattener apparatusused in the process of FIG. 1;

FIG. 4 is a perspective view of a divider apparatus according to theinvention;

FIG. 5 is a partial perspective view of the cylindrical cutter shown inFIG. 4;

FIG. 6 is partial front view, partly in section, of the left end of thedivider shown in FIG. 4; and

FIG. 7 is a front view of a battery plate element according to theinvention, with the concealed portion of the plate shown in phantom.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1, the process according to the invention is shown inrelation to the other steps conventionally used in a continuous processfor making lead-acid battery plates. The known process for making suchplates includes an initial step 21 of melting hog lead in a furnace,followed by a step 22 of feeding molten lead alloy to a strip caster.Trim from the caster is recycled to the furnace. The strip is coiled(23) on a winder, and coils of lead alloy strip are stored for lateruse.

To form a battery grid, the coil is unwound (24) and the free end is fedthrough an expander that cuts, slits and stretches (25) the strip toform a mesh-like pattern of grid elements. See, for example, theexpanders described in U.S. Pat. Nos. 4,315,356 and 4,291,443 assignedto Cominco Ltd., the contents of which are incorporated herein byreference. Trim from the expander is recycled to the furnace. Theexpanded strip is then pasted (26) by a conventional paster, and thenfed to the divider according to the invention, wherein the strip is cut(27). Plates cut from the strip are then flattened (28), then passed ona conveyer through an oven for flash-drying (29), and then stacked (30)for later use. Flash drying is performed using an open gas flame or anoven, for example, as a 10-15 second drying of the plates in aconventional blast drying oven at 260° C. (500° F.).

A shown in FIG. 2, a rotary divider 31 used in the cutting step has avacuum system 32 associated therewith. Divider 31 cuts the moving stripinto plates and, at the same time, cuts rounded corners as explained indetail below. Each pair of corners cut results in a small, roughlytriangular piece of trim (scrap metal.) Vacuum system 32 includes acyclone blower 33 connected to a cyclone 34 by a conduit 35. Cyclone 34is in turn connected to a pair of manifolds 36 disposed at opposite endsof divider 31 through a pair of hoses or pipes 37. The trimmed piecesfrom divider 31 enter manifolds 37 and pass through hoses 37 intocyclone 34. The pieces then fall out of the bottom of cyclone 34 into abarrel 38. The contents of barrel 38 may be periodically recycled to asmelter.

Referring now to FIGS. 3 and 4, the divider 31 is located immediatelyahead of a flattener 39. A pasted strip 41 has a series of regularlyspaced holes 42 which are engaged by lugs or dogs 43 of an optionalfirst drive roller 44. Roller 44 may comprise a series of spaced,coaxial disks of equal diameter that receive strip 41 from the paster,with lugs 43 being on the center disk. Strip 41 then moves over severalspaced, parallel support rails 46 into a nip 47 between a second driveroller 48 and a cylindrical cutter 49.

Cutter 49 simultaneously cuts strip 41 into two rows of battery plates41A having rounded outside (bottom) corners 51. A freely-rotatablerotary brush 52, for example, a 2-inch diameter nylon brush, contactsthe cylindrical outer surface of cutter 49 tangentially, preferably fromend to end, cleaning it and aiding in forcing the trim pieces into theinterior of cutter 49. All of rolls 44, 48 and 49 are driven by asuitable drive system 53 such as an electric motor provided with a gearlinkage (not shown) that ensures that rolls 44, 48 and 49 rotatetogether at the same speed.

Flattener 39 includes pair of upper and lower conveyer belts 56, 57wound over a series of spaced pairs of upper and lower rollers 58, 59and spaced apart by a distance approximately equal to the platethickness, e.g., 0.04 inch. The plates 41A are fed between belts 56, 57.The action of rollers 58, 59 flattens out any raised edges which mayhave formed during cutting. Rollers 58, 59 have an associated drivesystem but need not be biased to exert extra pressure on plates 41A.

FIGS. 4 to 6 illustrate the divider 31 in detail. Rotary cutter 49,which is preferably a cylindrical drum, has a plurality of cutter blades61 projecting radially from its cylindrical surface in a repetitivepattern that forms two offset rows of plates 41A. Blades 61 includelengthwise blades 61A that form the sides of each plate 41A, centraltransverse blades 61B for forming the tab on each plate, and roundedblades 61C for forming the rounded lower corners of each plate. Blades61B alternate with a row of central recesses 62 that mate with lugs 43of drive roller 48, and blades 61B alternately face in oppositedirections to produce two rows of plates 41A from a single strip asshown. Blades 61A extend from one end of a blade 61B alternately inoffset positions towards each end of the roll, at which point each bladesplits into a pair of curved, symmetrical blades 61C. Each pair ofblades 61C cuts off a roughly triangular piece from strip 41 to form apair of rounded corners 51.

Rotary cutter 49 has a pair of axles 63 projecting from its endsrotatably supported by a pair of bearings 64; drive roller (cuttinganvil) 48 is similarly supported. Cutter 49 further has a pair ofannular recesses 65 in each end. Each recess 65 communicates with aseries of spaced radial holes 66 each formed adjacent to and outwardlyof an associated pair of cutter blades 61C. Holes 66 are large than thepieces trimmed by the blades 61C.

The vacuum manifolds 36 are mounted in contact with the rotating ends ofcutter 49 covering each recess 65. Each manifold comprises a pair ofmating sections 36A, 36B which are secured together by any appropriatemeans, such as screws or other fasteners, on opposite sides of each axle63. Sections 36A, 36B have semicircular cutaway portions which form amanifold chamber 65A in communication with recess 65. An outlet opening65B in one section 36B allows cut-away corner pieces 67 to pass througha manifold extension 70 having a gradually reduced width, and then intohose 37, which is coupled to extension 70. For purposes of removingcorner pieces 67 from lead-acid SLI battery plates of conventional size,a minimum vacuum of about 9 inches of water is needed. If the processline is operating at a speed higher than about 100-130 feet/minute, astronger vacuum may be needed.

In operation, cutter 49 rotates to continuously cut plates 41A asdescribed above. Triangular trim pieces 67 are cut away from strip 41 byrounded blades 61C. These pieces 67 are drawn inwardly through holes 66by the suction applied by vacuum system 32 through manifolds 36. If thesuction is not sufficient to make each piece 67 fall in, brush 52contacts pieces 67 and presses them inwardly in combination with theforce of the suction. Pieces 67 enter annular recess 65 and theassociated manifold 36, after which they travel to barrel 38 viamanifold chamber 65A, outlet 65B, manifold extension 70, hose 37 andcyclone 34, as described above.

FIG. 7 illustrates a plate element 71 according to the inventionincluding a pasted plate 41A having rounded bottom corners 51, squaretop corners 72, and a conductive tab 73 extending from between the topcorners 72. The grid itself includes a generally rectangular outer frame74 and a mesh of grid elements 75 (see FIG. 1) spanning frame 74 whichare covered by the battery paste. Many different grid designs arewell-known in the art. Each plate 41A is disposed in a conventionalsubmicro polyethylene separator envelope 76. Envelope 76 is formed froma single piece of material which is folded in half and secured at theedges, for example, with crimped edges 77. During insertion orre-insertion of plate 41A into envelope 76, such as during the strapforming operation, rounded corners 51 prevent tearing of envelope 76.

It will be understood that the foregoing description is of preferredexemplary embodiments of the invention, and that the invention is notlimited to the specific forms shown. For example, the process andapparatus according to the invention could be used to manufacturevirtually any type of plate, and are not limited to the manufacture ofbattery plates. The holes, blades and recesses of the cutter could berearranged to cut away small pieces at locations other than the bottomcorners as disclosed. These and other modifications may be made in thedesign and arrangement of the elements without departing from the scopeof the invention as expressed in the appended claims.

We claim:
 1. In a battery plate for use in a lead-acid battery, theplate comprising a conductive grid covered with an active lead material,the grid comprising a generally rectangular outer frame having a pair ofsides, a top and a bottom spanned by grid elements forming a mesh, theframe having a pair of upper corners, a pair of lower corners, and anelectrically conductive tab extending from a location on the top of theframe between the two upper corners, the improvement which comprises:theplate has been formed by expanding a strip of lead alloy, and the twoupper corners are square and the two lower corners have a rounded shapelacking a sharp edge which would tend to cut an adjacent separatorelement, and the sides of the frame are substantially straight and freeof projections.
 2. A plate element for use in a lead-acid battery,comprising:a separator envelope joined along its sides and bottom endand having an open upper end; and a battery plate comprising aconductive grid formed by expanding a strip of lead alloy and having anactive lead material applied thereto, which plate is inserted into theseparator envelope bottom end first, wherein the grid comprises agenerally rectangular outer frame having a pair of sides, a top and abottom spanned by grid elements forming a mesh, the frame having a pairof upper corners and a pair of lower corners, with an electricallyconductive tab extending from a location on the top of the frame, theplate being substantially completely inserted into and covered by theenvelope except for the tab, which extends out of the open upper end ofthe envelope, and the two lower corners of the plate have a roundedshape lacking a sharp edge which would tend to cut the separatorenvelope.
 3. The plate of claim 1, wherein the tab extends from alocation between and spaced from the two upper corners.
 4. The plateelement of claim 2, wherein the upper corners of the frame are square.5. The plate element of claim 4, wherein the sides of the frame aresubstantially straight and free of projections.
 6. The plate element ofclaim 2, wherein the separator envelope has substantially the same shapeas the frame and is sealed along its bottom and sides so that the framefits closely therein with the tab projecting out of the open upper endof the separator envelope.
 7. The plate element of claim 6, wherein theseparator envelope consists essentially of polyethylene.
 8. The plateelement of claim 7, wherein the separator envelope consists essentiallyof a single piece of polyethylene folded in half along a bottom edgethereof and crimped along its sides.
 9. The plate element of claim 4,wherein the tab extends from a location between and spaced from the twoupper corners. .Iadd.
 10. A battery plate for use in a lead-acidbattery, the plate comprising:a conductive grid formed by expanding astrip of lead alloy and covered with an active lead material, the gridhaving a generally rectangular shape including a top and a bottom andsides, the top and bottom being spanned by grid elements formed a meshand the sides being substantially straight and free of projections, thegrid having a pair of substantially square upper corners formed in thetop, and a pair of rounded lower corners formed in the bottom, and aconductive tab extending from a location on the top between the twoupper corners. .Iaddend..Iadd.11. A battery plate for use in a lead-acidbattery, the plate comprising: a conductive grid formed by expanding astrip of lead alloy and covered with an active lead material, the gridhaving a generally rectangular shape including a top and a bottom andsides, the top and bottom being spanned by grid elements forming a meshand the sides being open cut mesh and substantially straight and free ofprojections, the grid having a pair of substantially square uppercorners formed in the top, and a pair of rounded lower corners formed inthe bottom, and a conductive tab extending from a location on the topbetween the two upper corners. .Iaddend..Iadd.12. A battery plate foruse in a lead-acid battery, the plate comprising: a conductive gridformed by expanding a strip of lead alloy and covered with an activelead material, the grid having a generally rectangular shape including atop and a bottom, the top and bottom being spanned by grid elementsforming a mesh, the grid having a pair of substantially square uppercorners formed in the top, and a pair of rounded lower corners formed inthe bottom, and a conductive tab extending from a location on the topbetween the two upper corners, and a separator substantially completelyenveloping the plate except for the tab which extends from an openportion of the separator, the separator being sealed at least along sideportions thereof so that the plate fits closely therein. .Iaddend.